Numerous amphibious aircraft are provided with deformable parallelogram landing gear. The term deformable parallelogram is used for a deformable structure with four parallel articulations even though, in practice, pairs of sides of the structure are very often not of identical length.
Examples are aircraft such as the Grumman Widgeon or the Grumman Goose. The latter includes two panels hinged on the aircraft structure about parallel first axes, a casing being hinged to each of the panels about second axes parallel to the first axes. The casing carries a wheel at its lower end. The assembly may be retracted in the manner of a deformable parallelogram, the wheel remaining parallel to itself during retraction.
The Boeing C17 military transport aircraft is also equipped with main landing gear of the deformable-parallelogram type. In such landing gear, the casing receives a pivot with a substantially vertical pivot axis, the pivot receiving at its bottom part a rocker arm carrying the wheels and at its top part the damper connected to the rocker arm. A linkage enables the pivot, and thus the rocker arm, the damper and the wheels, to be turned during retraction or deployment of the landing gear.